1. Field of the Invention
The invention is related to the field of magnetic disk drive systems and, in particular, to a perpendicular magnetic recording medium having an interlayer formed from multiple layers. More particularly, the interlayer is formed from a layer of FCC material (e.g., NiWCr), a layer of BCC material (e.g., Cr), and a layer of HCP material (e.g., Ru).
2. Statement of the Problem
One type of recording medium presently used in magnetic recording/reproducing apparatuses is a longitudinal magnetic recording medium. A longitudinal magnetic recording medium includes a magnetic recording layer having an easy axis of magnetization parallel to the substrate. The easy axis of magnetization is the crystalline axis that is aligned along the lowest energy direction for the magnetic moment. Another type of recording medium is a perpendicular magnetic recording medium. A perpendicular magnetic recording medium includes a magnetic recording layer having an easy axis of magnetization oriented substantially perpendicular to the substrate. Hexagonal-close-packed (HCP) Co-alloys are typically used as the magnetic recording layer for both longitudinal and perpendicular recording. The easy axis of magnetization for these materials lies along the c-axis or <0001> direction.
The perpendicular magnetic recording medium is generally formed with the following layers on a substrate, a soft magnetic underlayer (SUL), an interlayer, a perpendicular magnetic recording layer, and a protective layer for protecting the surface of the perpendicular magnetic recording layer. The soft magnetic underlayer (SUL) serves to concentrate a magnetic flux emitted from a main pole of a write head and to serve as a flux return path back to a return pole of the write head during recording on the magnetic recording layer. The interlayer serves to control the size of magnetic crystal grains and the orientation of the magnetic crystal grains in the magnetic recording layer. The interlayer also serves to magnetically de-couple the SUL and the magnetic recording layer.
The interlayer may be formed from a single layer of material, such as a layer of Ru that has an HCP structure. The interlayer may alternatively be formed from multiple layers. For example, a common interlayer comprises a layer of Ru formed on a seed layer, such as Ta, NiFe, NiW, etc. The seed layer is commonly formed from a face-centered-cubic (FCC) material with the layer of Ru (having the HCP structure) formed on the FCC material. One particular interlayer comprises a seed layer of NiW or another Ni-based alloy, a first layer of Ru deposited at a lower pressure, and a second layer of Ru deposited at a higher pressure.
One problem with many present interlayers for perpendicular magnetic recording media is that they include significant amounts of Ru, which is an HCP material. The thickness of Ru in a common interlayer can reach 200 Å or more. As the cost of Ru and other HCP materials increases, the cost of fabricating perpendicular magnetic recording media unfortunately also increases.